Table 1. Nutrients of interest utilised by C. difficile during gut colonisation.

Nutrient	Metabolic pathway	Metabolic end product(s)	Genes	Reference
Proline	Stickland metabolism	5-aminovalerate + NAD+	prd operon	[20,22]
Glycine	Stickland metabolism	Acetate + NAD+ + ATP	grd operon	[20,22]
Hydroxyproline	Stickland metabolism	5-aminovalarte + NAD+	hypD and prd operon	[23]
Ornithine	Stickland metabolism	NADH + Ammonia + Acetyl-CoA + Alanine	orr, oraSE, ord, and ortAB	[24]
CO2	Wood–Ljungdahl pathway	Acetyl-CoA + Acetate	acsA, cooC, fhs, fchA, folD, metV, metF, gcvL, acsF, acsD, acsC, acsE, acsB, gcvH, acsV	[25]
Ethanolamine	Central carbon metabolism	Ethanol + Acetyl-CoA + Acetate	eut gene cluster	[26]
Sorbitol	Carbohydrate metabolism	Fructose-6-phosphate + NADH	srlR, srlM, srlAebB, and srlD	[27]
Trehalose	Carbohydrate metabolism	Glucose + Glucose-6-phosphate	treA, treR and/or treA2, ptsT, treX, and treR2	[28,29]
Cellobiose	Carbohydrate metabolism	Glucose + Glucose-6-phoshate	celR, celA, celB, celF, and celC	[30]
Sialic acid (5-acetylneuraminate)	Carbohydrate metabolism	Pyruvate, Acetate + Fructose-6-phosphate	nanE, nanA, nanT, and nanK	[31]
Mannose	Carbohydrate metabolism	Fructose-6-phosphate	CD630_24910, CD630_02860–02890	[32]
Zinc	N/A	N/A	zupT	[33]
Tyrosine	Stickland metabolism	p-cresol	hpdBCA operon	[34,35]